MCQs
Total Questions : 71
| Page 4 of 8 pages
Answer: Option A. -> 2 and 3
Answer: (a).2 and 3
Answer: (a).2 and 3
Answer: Option D. -> Exponentially
Answer: (d).Exponentially
Answer: (d).Exponentially
Answer: Option D. -> 0.006846
Answer: (d).0.006846
Answer: (d).0.006846
Question 34. A mercury thermometer with bulb idealized as a sphere of 1 mm radius is used for measuring the temperature of fluid whose temperature is varying at a fast rate. For mercury
k = 10 W/m K
α = 0.00005 m²/s
h = 10 W/m² K
If the time for the temperature change of the fluid is 3 second, what should be the radius of thermocouple to read the temperature of the fluid?
For the thermocouple material
k = 100 W/m K
α = 0.0012 m²/s
h = 18 W/m² K
k = 10 W/m K
α = 0.00005 m²/s
h = 10 W/m² K
If the time for the temperature change of the fluid is 3 second, what should be the radius of thermocouple to read the temperature of the fluid?
For the thermocouple material
k = 100 W/m K
α = 0.0012 m²/s
h = 18 W/m² K
Answer: Option A. -> .864 mm
Answer: (a)..864 mm
Answer: (a)..864 mm
Question 35. A thermocouple junction of spherical form is to be used to measure the temperature of the gas stream. The junction is at 20 degree Celsius and is placed in a gas stream which is at 200 degree Celsius. Make calculations for junction diameter needed for the thermocouple to have thermal time constant of one second. Assume the thermos-physical properties as given below
k = 20 W/ m K
h = 350 W/m² K
c = 0.4 k J/kg K
p = 8000 kg/m³
k = 20 W/ m K
h = 350 W/m² K
c = 0.4 k J/kg K
p = 8000 kg/m³
Answer: Option C. -> 0.656 mm
Answer: (c).0.656 mm
Answer: (c).0.656 mm
Question 36. A flat wall of fire clay, 50 cm thick and initially at 25 degree Celsius, has one of its faces suddenly exposed to a hot gas at 950 degree Celsius. If the heat transfer coefficient on the hot side is 7.5 W/m² K and the other face of the wall is insulated so that no heat passes out of that face, determine the time necessary to raise the center of the wall to 350 degree Celsius. For fire clay brick
Thermal conductivity = 1.12 W/m K
Thermal diffusivity = 5.16 * 10¯⁷ m²/s
Thermal conductivity = 1.12 W/m K
Thermal diffusivity = 5.16 * 10¯⁷ m²/s
Answer: Option A. -> 43.07 hours
Answer: (a).43.07 hours
Answer: (a).43.07 hours
Answer: Option B. -> False
Answer: (b).False
Answer: (b).False
Question 38. A thermocouple junction of spherical form is to be used to measure the temperature of the gas stream. The junction is at 20 degree Celsius and is placed in a gas stream which is at 200 degree Celsius. Make calculations for time required by the thermocouple to reach 197 degree Celsius temperature. Assume the thermos-physical properties as given below
k = 20 W/ m K
h = 350 W/m² K
c = 0.4 k J/kg K
p = 8000 kg/m³
k = 20 W/ m K
h = 350 W/m² K
c = 0.4 k J/kg K
p = 8000 kg/m³
Answer: Option D. -> 4.094 seconds
Answer: (d).4.094 seconds
Answer: (d).4.094 seconds
Answer: Option C. -> 63.3
Answer: (c).63.3
Answer: (c).63.3
Answer: Option A. -> 0.04 to 2.5 seconds
Answer: (a).0.04 to 2.5 seconds
Answer: (a).0.04 to 2.5 seconds